Voltridia Island

Voltridia Island is one of the outlying islands beyond the Roria Town Map. It's a rugged mountain with storm clouds surrounding its peak. To come here, the player is required to do Port Decca's side quest before taking the Voltiac Ticket and travelling to this island.

The island is more like Obsidia Island than anything else, considering that the two mountains are the same color and that the beaches both have black sand. However, their differences cannot be ignored. Voltridia's peak is dark and stormy, while Obsidia's is quite like that of a volcano. Also, the sides of the mountains are jagged and smooth, respectively.

The Wild Pokémon of Voltridia stay inside its cavern, which also houses a certain Legendary Trio member.

Voltridia Cavern Entrance
The island itself is nothing special- the real deal is the entrance it contains. It is a large hole in the side of the mountain facing Salty Sam. Some species of Electric-type Pokémon can be found inside Voltridia Cavern, mostly seen before. There's one or two new faces in the cavern, though, including an Alolan Form of a certain Pokémon. The main reason that players come here, though, is to catch the Legendary Bird living inside.

Trivia

 * Despite being surrounded by the sea, players can neither surf nor fish. This is also the case on Frigidia and Obsidia Islands.